Medical devices adapted for implantation into body lumens that support fluid flow are well known and commercially available. One such device is the self-expandable stent of the type disclosed in the Wallsten U.S. Pat. No. 4,655,771. Stents of this type can be used to treat vascular stenosis and to maintain openings in the urinary, bilary, esophageal, tracheal and bronchial tracts of a patient. Self-expanding stents are generally comprised of a plurality of resilient filaments that are helically wound and interwoven to form a porous lattice. The stents assume a generally tubular form having a first diameter in an unloaded state, but can be forced into a reduced-diameter, extended length form (i.e. the "loaded" state) by inwardly-directed radial forces.
Another type of medical device adapted for implantation into a body lumen is an occlusion device designed to occlude a body lumen and thus stop fluid flow though the body lumen. One such occlusion device is described in the commonly assigned and co-pending U.S. patent application Ser. No. 08/797,983, which is expressly incorporated herein by reference in its entirety for all purposes. Occlusion devices of this type can be used to control internal bleeding, bypass a lumen, relieve the pressure created by an aneurysm in a lumen, or stop the flow of fluid to a tumor in a lumen.
Occlusion devices of the type shown and disclosed in application Ser. No. 08/797,983 are comprised of a self-expandable support structure and a flexible fluid flow-occluding membrane attached to the support structure. The support structure can be formed from any self-expanding means, including a number of filaments that are interwoven in a manner similar to that described in the Wallsten U.S. Pat. No. 4,655,771. Alternatively, the support structure can be comprised of etched or machined self-expanding tubes formed from nitinol or spring steel, such as those marketed under the tradename "Symphony" from MediTech, or other designs utilizing a plurality of zig-zag formed spring steels and the like. The membrane can be interwoven with at least portions of the support structure, or it can be formed separately from the support structure and attached to a portion of the interior or exterior surface of the support structure. The membrane can be fabricated from a micro-porous or non-porous material. Similar to self-expanding stents, the occlusion device assumes a substantially tubular shape in an unloaded, expanded state, and can be forced into a reduceddiameter, extended-length shape when subjected to inwardly directed radial forces. The occlusion device further includes a constricted region, which can be formed in either the membrane alone or in both the membrane and the support structure. The constricted region of the occlusion device is "closed" to fluid flow, and in this manner, the device occludes the lumen in which the occlusion device is implanted to restrict fluid flow through the lumen.
Methods for implanting medical devices in a body lumen are also known. A delivery system having proximal and distal ends and comprising an outer sheath, an inner catheter having a pointed tip, and a plunger is often used to deploy a self-expanding stent at the desired treatment location in a body lumen. The stent is compressed into its reduced-diameter state, and is held in its compressed state at the end of the inner catheter between the pointed tip and the plunger by the outer sheath of the delivery system. Such a delivery system can be inserted into a body lumen and tracked radiographically by monitoring the position of a radiopaque marker positioned on the outer sheath to guide the delivery system to the desired treatment location. As the system is guided through the lumen, the pointed tip of the inner catheter expands the body lumen in advance of the delivery system to ease navigation. A guide wire that extends through the inner catheter along the length of the outer sheath can also be used to aid in moving the delivery system through the lumen. When positioned at the treatment site, the stent is deployed by retracting the outer sheath, which releases the stent and allows it to self expand and engage the body lumen. After the outer sheath has been retracted and the stent is fully expanded, the inner catheter and pointed tip can be withdrawn back through the interior of the stent.
Such a delivery system can be difficult to use with occlusion devices such as those described above, however. Because such occlusion devices include a constricted region, it is difficult to withdraw the inner catheter and pointed tip through the constricted region when the occlusion device has been deployed at the treatment site. A delivery system having an outer sheath and a plunger without an inner catheter and pointed tip (i.e. an "open" delivery system) can more efficiently be used to deploy such a medical device. An open delivery system, however, may encounter difficulty in navigating the body lumen due to the tortuous nature of lumens. It is thus highly desirable to include a tip or a guide member that dilates the body lumen at the distal end of a delivery system used to deliver and deploy a medical device having a constricted region. A need therefore exists for an improved medical device delivery system that includes a guide member for dilating body lumens, yet is capable of being efficiently used with medical devices having a constricted region.